Lymphoid B cells upregulate HIV-1 ex vivo and are linked to its expression in vivo

B cell follicles in secondary lymphoid tissues are major sites of HIV expression in untreated people living with HIV (PLWH), but whether lymphoid B cells promote HIV expression in CD4+T cells is unknown. Using a tonsil model and flow cytometry, germinal center B cells induced HIV expression in follicular helper CD4+T cells (TFH) in a concentration-, contact-, and major histocompatibility complex class II (MHC-II)dependent manner. Non-naïve tonsil B cells also induced HIV expression in nonTFH CD4+T cells that was MHC-II restricted. In situ hybridization and immunofluorescent staining of lymph node sections from six PLWH on long-term antiretroviral therapy (ART) and six ART-naïve PLWH demonstrated most HIV RNA-expressing (vRNA+) cells were adjacent to at least one B cell. In both groups, vRNA+ cells per mm² were elevated in B cell follicles, particularly after adjusting for CD3+CD4+frequencies. TFH (PD-1+BCL6+) were a minority of vRNA+ cells in all PLWH. In contrast to ART-naïve PLWH, most vRNA+ cells in PLWH on ART resided outside follicles, and were preferentially adjacent to extrafollicular B cells. Thus, B cells upregulate HIV expression largely through cognate interactions in vitro and are linked to HIV expression in secondary lymphoid tissues.